In Asterisk 11.x before 11.25.3, 13.x before 13.17.2, and 14.x before 14.6.2 and Certified Asterisk 11.x before 11.6-cert18 and 13.x before 13.13-cert6, insufficient RTCP packet validation could allow reading stale buffer contents and when combined with the "nat" and "symmetric_rtp" options allow redirecting where Asterisk sends the next RTCP report.
https://issues.asterisk.org/jira/browse/ASTERISK-27274
http://www.debian.org/security/2017/dsa-3990
http://downloads.asterisk.org/pub/security/AST-2017-008.html